High-field pulsed EPR spectroscopy for the speciation of the reduced [PV2MO10O40]6- polyoxometalate catalyst used in electron-transfer oxidations

Ilia Kaminker, Hila Goldberg, Ronny Neumann, Daniella Goldfarb

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Abstract

An in-depth spectroscopic EPR investigation of a key intermediate, formally notated as [PVIVVVMo10O40] 6- and formed in known electron-transfer and electrontransfer/oxygen- transfer reactions catalyzed by H5PV2Mo10O 40, has been carried out. Pulsed EPR spectroscopy have been utilized: specifically, W-band electron-electron double resonance (ELDOR)-detected NMR and two-dimensional (2D) hyperfine sub-level correlation (HYSCORE) measurements, which resolved 95Mo and 17O hyperfine interactions, and electron-nuclear double resonance (ENDOR), which gave the weak 51V and 31P interactions. In this way, two paramagnetic species related to [PVIVVVMo10O40]6- were identified. The first species (30-35%) has a vanadyl (VO2+)-like EPR spectrum and is not situated within the polyoxometalate cluster. Here the VO2+ was suggested to be supported on the Keggin cluster and can be represented as an ion pair, [PVVMo10O39] 8--[VIVO2+]. This species originates from the parent H5PV2Mo10O40 in which the vanadium atoms are nearest neighbors and it is suggested that this isomer is more likely to be reactive in electrontransfer/oxygen-transfer reaction oxidation reactions. In the second (70-65 %) species, the VIV remains embedded within the polyoxometalate framework and originates from reduction of distal H5PV2Mo10O40 isomers to yield an intact cluster, [PVIVVVMo10O 40]6-.

Original languageEnglish
Pages (from-to)10014-10020
Number of pages7
JournalChemistry - A European Journal
Volume16
Issue number33
DOIs
Publication statusPublished - Sep 3 2010

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Keywords

  • ENDOR spectroscopy
  • EPR spectroscopy
  • Electron transfer
  • Polyoxometalates
  • Vanadium

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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